1. Field of the Invention
The present invention relates to a method for evaluating spectrum utilization efficiency in a radio system sharing frequency; and, more particularly, to a method for evaluating spectrum utilization efficiency based on frequency sharing technology when a Digital television (DTV) system in a TV band shares a frequency with a cognitive radio system of a spectrum overlay technique.
This work was supported by the IT R&D program for MIC/IITA [2005-S-046-03, “Development of the basic spectrum resource utilizing technology”].
2. Description of Related Art
According to development of radio communication technology and introduction of a new wireless communication service, it is required to efficiently use limited frequency resources. A method for maximizing spectral efficiency and a method for minimizing interference with another wireless communication system through performance optimization of the wireless communication system, e.g., multiple access, coding technology, modulation efficiency, and information compression technology, are used in order to increase spectrum utilization efficiency.
As another access method having a different approach from those of the above methods, frequency sharing technology for increasing spectrum utilization efficiency in a frequency band in use has been studied. As shown in FIG. 1, the frequency sharing technology includes a spectrum underlay method where a secondary user shares spectrum without interfering existing users with very low power density, which is similar to the noise floor as shown in FIG. 1, by using a wide frequency band, and a spectrum overlay method where the secondary user shares the frequency without interfering a primary licensee in case that the primary licensee does not use the frequency.
Ultra wide band technology is the representative example of the spectrum underlay method. Cognitive radio technology is the representative example of the spectrum overlay technique.
In Institute of Electrical and Electronics Engineers (IEEE) 802.22 Wireless Regional Area Network (WRAN) working group, which is an International Organization for Standardization, standardization related to the cognitive radio technology for increasing spectrum utilization efficiency in the TV band is being discussed actively.
An index showing spectrum utilization efficiency is required to evaluate the spectrum utilization efficiency of the radio system. The spectrum utilization efficiency of the radio system defined in ITU-R SM. 1046 recommendation and National Telecommunications and Information Administration (NTIA) report from USA may be expressed as follows:
      S    ⁢                  ⁢    U    ⁢                  ⁢    E    =      M          B      ×      S      ×      T      where M represents the quantity of transmitted information; B represents a radio bandwidth; S represents a geometrical space where the wireless communication system is serviced, which is generally a wireless communication coverage region; and T represents a service time.
The definition on the spectrum utilization efficiency described above is generally applied to all radio systems. However, since diverse radio systems have different characteristic features, the methods showing the spectrum utilization efficiency may be differed. For example, since the main object of a point-to-point micro wave radio system is long-distance signal transmission, a transmission/reception distance is added as a main element. In case of broadcasting, a service region is added as a main element.
The above conventional spectrum utilization efficiency index is used to evaluate the spectrum utilization efficiency on the specific wireless communication system, e.g., channel capacity, which is used in a given frequency band without considering the frequency share environment. In particular, in case of sharing the frequency band in use according to the overlay frequency sharing method such as a cognitive radio system, it is not proper to evaluate spectrum utilization efficiency by using the conventional spectrum utilization efficiency evaluation index.
In other words, it is difficult to evaluate spectrum utilization efficiency by frequency sharing of the DTV system and the cognitive radio system of the spectrum overlay technique in the TV band with channel capacity per coverage area used to evaluate spectrum utilization efficiency of the general wireless communication system or the conventional spectrum utilization efficiency evaluation index such as the coverage area per frequency used to show the spectrum utilization efficiency of the broadcasting system.